Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C201/00—Preparation of esters of nitric or nitrous acid or of compounds containing nitro or nitroso groups bound to a carbon skeleton
  • C07C201/06—Preparation of nitro compounds
  • C07C201/08—Preparation of nitro compounds by substitution of hydrogen atoms by nitro groups

Definitions

• the invention relates to a process for the preparation of 2,3-dichloro-nitrobenzene by nitration of 1,2-dichloro-benzene using an anhydrous mixture of nitric acid, sulphuric acid and phosphoric acid as the nitrating medium.
• Dichloro-nitrobenzenes are important intermediates for the synthesis of pharmaceuticals and plant protection agents.
• the currently known processes for the nitration of 1,2-dichlorobenzene give a mixture of 2,3-dichloro-1-nitrobenzene and 3,4-dichloro-1-nitrobenzene.
• the market demand for the two compounds is subject to changes. Thus, there was a greater need hitherto for the 3,4-isomer. Under the nitrating conditions practised hitherto the formation of this isomer was favoured so that production could follow the market demand.
• DE-OS German Published Specification 2,422,305 describes a process in which the reaction is carried out using 90% strength nitric acid as the nitrating agent and in a nitrating medium consisting of phosphoric acid and sulphuric acid. Using this process, the ratio of the para to the ortho isomer can be shifted from 1.63 to 1.2.
• the said DE-OS ( German Published Specification ) '305 does not indicate a concentration of the phosphoric acid; it may therefore be suspected that commercially available, 85% strength by weight phosphoric acid is used.
• the said DE-OS (German Published Specification) '305 does not give any yields and any data for dinitration. According to our own investigations, the yields according to this process are only about 80% of the theoretical yield.
• 104% strength H 3 PO 4 signifies a concentrated, i.e. dehydrated, phosphoric acid, which contains a proportion of pyrophosphoric acid and accordingly has a P 2 O 5 content which corresponds to 104% H 3 PO 4 .
• the serious disadvantage of such a procedure is the great fall in the yield to 89% or even 86% as a specific function of the reaction temperature.
• the process according to the invention is characterised by the use of an anhydrous nitrating acid mixture.
• a nitrating acid mixture can be prepared by mixing together industrially available, nearly anhydrous acids, provided one of the acids is employed with an anhydride content which is suitable to use up the small water content of the two other acids.
• the reaction can be carried out, for example, by use of a 98% strength HNO 3 and a 98% strength H 2 SO 4 if the phosphoric acid is an acid which has been concentrated in the manner described above, which thus contains a proportion of pyrophosphoric acid, which corresponds to a content of acid anhydride P 2 O 5 which exceeds the content of the 100% strength H 3 PO 4 .
• nitric acid and a phosphoric acid with a low water content are employed, if at the same time, instead of the sulphuric acid, oleum is employed whose content of SO 3 is suitable to use up the water entrained by the other acids.
• oleum is employed whose content of SO 3 is suitable to use up the water entrained by the other acids.
• HNO 3 if the phosphoric acid is employed in the form of the concentrated acid and/or the sulphuric acid in the form of oleum.
• Further modifications of this composition of the nitrating acid mixture are known in expert manner when only the indication of the freedom from water in the acid mixture is fulfilled.
• the nitric acid and the sulphuric acid are employed as industrially available approximately 98% strength acids and the phosphoric acid is employed in the form of a concentrated acid. It is self-evident that phosphoric acid and/or sulphuric acid with a content of anhydride can also be employed in the manner described above in an amount which exceeds the consumption of the water entrained by the other acid (the other acids).
• a nitrating acid mixture which still contains a proportion of anhydride in the form of pyrophosphoric acid is also an anhydrous acid mixture within the meaning of the present invention.
• the molar mixing ratio of sulphuric acid and phosphoric acid assumes values from 0.05 to 3 mol of H 2 SO 4 : 1 mol of H 3 PO 4 , preferably 0.1 to 1.5 mol of H 2 SO 4 : 1 mol of H 3 PO 4 , very particularly preferably from 0.12 to 0.5 mol of H 2 SO 4 : 1 mol of H 3 PO 4 .
• the process according to the invention is carried out at a reaction temperature of 30 to 180° C., preferably 60 to 140° C. particularly preferably 75 to 125° C.
• a reaction temperature of 30 to 180° C., preferably 60 to 140° C. particularly preferably 75 to 125° C.
• the molar ratio of the nitric acid to the dichlorobenzene is 0.7 to 1.4: 1, preferably 0.85 to 1.3: 1, very particularly preferably 1.0 to 1.2: 1.
• a phase separation in general occurs into an upper organic phase and a lower acid phase.
• the isomer mixture of 2,3-dichloro-nitrobenzene/3,4-dichloro-nitrobenzene contained therein is worked up by means of further aqueous work-up (removal of residual acid) and separated into the two isomers by customary methods, such as distillation, crystallisation or chromatography.
• the lower acid phase obtained in this work-up can be freed from the water of reaction from the nitration reaction by distillation, preferably under reduced pressure, and as a result an anhydrous mixed acid, consisting essentially of sulphuric acid and phosphoric acid, can again be prepared.
• anhydrous mixed acid consisting essentially of sulphuric acid and phosphoric acid.
• Example 1 The process of Example 1 was repeated with the difference that the 80.5% strength or 98% Strength H 2 SO 4 was replaced by 1.64 mol or 1.31 mol of H 3 PO 4 concentrated to 104% (fictitious H 3 PO 4 content as a result of removal of H 2 O and formation of H 4 P 2 O 7 ) and the nitration temperature was increased to 85 to 110° C.
• the acid phase was then subjected to incipient distillation at 20 mm Hg column up to a bottom temperature of 180° C. and then temperature-controlled for 3 h.
• the loss in the concentrated waste acid was compensated by addition of fresh 104% strength H 3 PO 4 and the acid worked up in this way was employed again in the next nitration.

Priority Applications (1)

Applications Claiming Priority (4)

Related Parent Applications (1)

Publications (1)

Family

ID=6464362

Family Applications (1)

Country Status (4)

Cited By (3)

Citations (7)

• 1992
  • 1992-07-29 DE DE4225023A patent/DE4225023A1/de not_active Withdrawn
• 1993
  • 1993-07-16 DE DE59305115T patent/DE59305115D1/de not_active Expired - Fee Related
  • 1993-07-16 EP EP93111463A patent/EP0581148B1/de not_active Expired - Lifetime
  • 1993-07-23 JP JP5202086A patent/JPH06157427A/ja active Pending
• 1995
  • 1995-01-06 US US08/369,560 patent/US5475163A/en not_active Expired - Fee Related

Patent Citations (9)

Non-Patent Citations (3)

Also Published As

Similar Documents

Legal Events